1. Field of the Invention
The present invention relates to an ink-jet printhead and an ink expelling method. More particularly, the present invention relates to an ink expelling method using a laser and an ink-jet printhead utilizing the method.
2. Description of the Related Art
Typically, ink-jet printheads are devices for printing a predetermined image, color or black, by ejecting a small volume droplet of printing ink at a desired position on a recording sheet. In such ink-jet printheads, ink ejection mechanisms are largely categorized into two types depending on which ink droplet ejection method is used. One type of conventional ink-jet printhead is a thermally driven ink-jet printhead in which a heat source is employed to generate bubbles in ink to cause ink droplets to be ejected by an expansion force of the generated bubbles. However, the thermally driven type, in which ink is boiled to generate bubbles, requires excess energy. In addition, there is a limitation on the type of ink used.
In addition to the above-described ink droplet ejection mechanism, a variety of different ink droplet ejection mechanisms are conventionally used in ink-jet printheads, and one example is shown in FIG. 1.
Referring to FIG. 1, a piezoelectric crystal 15 having a concave surface and a convex surface is installed under a surface of ink 14. One electrode 16 is provided on the concave surface of the piezoelectric crystal 15 and three electrodes 17, 18, 19 are provided on the convex surface of the piezoelectric crystal 15. The piezoelectric crystal 15 produces sonic energy, and an acoustic pressure generated by the sonic energy vibrates the surface of the ink 14. If the acoustic pressure exceeds a surface tension of the ink 14 and atmospheric pressure, ink droplets A-E are expelled from the surface of the ink 14 through a hole in a plate 13. Selective combinations of the electrodes 16, 17, 18, and 19 control an expelling direction of each of the droplets A-E. However, the above-described expelling method presents a problem due to a complex structure thereof because the hemispherical piezoelectric crystal 15 and the electrodes 16, 17, 18, 19 should be installed under the surface of the ink 14.
FIG. 2 illustrates another conventional printhead based on an ink droplet expelling mechanism using a laser.
Referring to FIG. 2, a printhead 40 includes chambers 37C, 37M, 37Y containing multiple colored inks 22C, 22M, 22Y, a semiconductor laser 28 for selectively irradiating a laser beam L onto the inks 22C, 22M, 22Y, and a condenser lens 29 which converges the laser beam L. The laser beam L emitted from the semiconductor laser 28 is selectively irradiated through the condenser lens 29 onto the inks 22C, 22M, 22Y contained in the chambers 37C, 37M, 37Y. Accordingly, the inks 22C, 22M, 22Y evaporate and the evaporating inks 32C, 32M, 32Y move to a recording sheet of paper 50. This ink expelling method, however, is disadvantageous in that control of the procedure is complex and a large amount of energy is consumed.
Other conventional ink expelling mechanisms include an ink expelling mechanism in which a buffered solution is boiled using a laser and ink is expelled by vibrations caused by the boiling of the buffered solution. This mechanism also has similar problems in that the structure of the ink-jet printhead is complex and a large amount of energy is consumed.